Bone fractures occur in the general population due to trauma or bone diseases. Plaster or fiberglass casts have been employed for the treatment of most bone fracture patients. Traditional orthopedic casts or orthoses are produced by a body-based contacting model. The bottom mold for the cast is generated from surface shapes of injury limbs and filled up with plasters. Thermoplastic material, PE (Polyethylene) or CPP (copolymer polypropylene), is pasted on the mold and removed after it is cooled down. Bone fracture patients wear plaster splints after the surgery followed by orthoses for further recovery. Those casts may cause several skin diseases and a potential bone and joint injury due to their heavy structure and poor ventilation. Moreover, patients suffer mechanical pressures during the mold manufacture, and multi-reproduction of physical molds is unfeasible.
3D printing technology is a rapid growing manufacture technique for producing complex physical model using 3D digital model. Recently, the 3D printing technology has been extensively applied to surgical practices and medical training. The rapid manufacture of the physical model from medical images provides a technical means that results in minimal invasion in medical planning and treatment. Custom made rehabilitation tools produced using 3D printing technique has been deployed in the new development of orthoses.
Some novel concepts have been proposed as potential substitutes for plaster cast manufactured by the 3D printing technology. The mesh-like structure forms an artistic surface pattern of the model by changing its webby density, providing more solid fracture region with less material in healthy areas.
Another development is a model similar to Cortex but embedded with an ultrasound device for promoting the therapeutic process. Those new designs are fabricated using the 3D printing technique and environment friendly material. The cast geometries are generated from 3D scan models that are patient specific and are capable of offering wearing comfort and fashionable appearance. The mesh-like structure of the model presents excellent ventilation and significantly light weight. However, the mesh-like structure has less strength in supporting the injured limbs. Low intensity mechanical impact may break the webby beam. In addition, the webby shape is most likely to cause crack and fatigue due to the slender connecting bar.
A hybrid model for custom-fit wrist orthoses combines the webby frame with the shell cover to enhance the structural strength of the cast and to keep the ventilation of the cast. The design process mainly includes a process of modeling an inner frame and an outer cover via a CAD system. This approach may increase the stiffness of the model and prevent the model structure from breakage. However, an experienced CAD engineer is required for creating appropriate engineering structure.
Despite the technical advance and economic potential, 3D printing technologies have not become a primary means in fabrication of the orthopedic cast. Significant technical expertise is required for designing the cast, which is costly and timeconsuming. In order to perform a CAD process, the scanned data of subject limbs must be converted into a specific CAD file with geometric modifications. An experienced CAD engineer is required for creating the model and converting the model CAD file to an STL (Standard Template Library) file for 3D printing.
Clinical demands for developing a cast with good ventilation, light weight, and automatic design process and less requirements of expertise, have gotten more and more attention. The medical applications of the 3D printing are increasing due to its manufacture speed and cost effectiveness. The growing 3D printing technologies make it possible to fabricate a complex geometric model in orthopedic casts and significantly reduce the manufacturing time and cost.